1. Field of the Invention
The present invention relates to information recording methods and information recording apparatuses with respect to various recording media such as CD-Rs, CD-RWs, DVD-Rs, DVD-RWs, DVD-RAMs and DVD+RWs.
2. Description of the Related Art
Recently, optical disk drives capable of recording, such as CD-R drives, have come into practical use, and studies have been conducted in order to further increase the capacity and recording speed. Recordable optical disk media include: recordable optical disks using, for example, a dye medium; and rewritable disks using, for example, a magnetic optical medium or a phase change medium.
A general optical disk recording apparatus includes a semiconductor laser as a light source and emits on a recording medium a laser beam subjected to pulse-modulation by recording information, thereby forming a recording mark. On this occasion, the forming state of a recording mark varies depending on the power of the recording laser beam. Hence, conventionally, in order to obtain a recording power suitable for the characteristics of a recording medium, the so-called OPC (Optimum Power Control) method has been used in which test writing is previously performed on a predetermined area (PCA: Power Calibration Area) while varying the recording power as preparation for starting recording, and after the test writing, the power used for recording an area where a reproduction signal of the best quality is obtained is selected as the optimum recording power. When actually recording data, recording is performed while maintaining the optimum recording power thus obtained.
As for quality evaluation methods of the reproduction signal, several methods have been proposed, and the following method has been in practical use as a typical method.
First, there is a method (hereinafter appropriately referred to as “the β method”) that makes evaluation from asymmetry β of the reproduction signal. That is, as shown in FIG. 6, a positive peak value A (=Ipk−Idc) and a negative peak value B (=Idc−Ibt) with respect to the DC level of the reproduction signal are detected, and the asymmetry β is calculated byβ=((Ipk−Idc)−(Idc−Ibt))/(Ipk−Ibt).The reproduction signal having the asymmetry β of a predetermined value (for example, 0) is considered to be good.
Second, there is a method (hereinafter appropriately referred to as “the γ method”) that makes evaluation by using a degree of modulation m of the reproduction signal. First, as shown in FIG. 6, a maximum value Ipk and a minimum value Ibt of the reproduction signal are detected, and the degree of modulation m is calculated bym=(Ipk−Ibt)/Ipk.Next, based on the calculated degree of modulation m and recording power P then, a rate of change γ of the degree of modulation m with respect to recording power P is calculated byγ=(dm/dP)(P/m)Then, recording power Pt with which the rate of change γ becomes a predetermined value γt is obtained, and an optimum recording power is determined by multiplying the recording power Pt by a predetermined coefficient k.
On the other hand, recording methods of optical disks such as CDs and DVDs adopt a mark edge recording method in which the length of a mark represents information, which method is suitable for achieving high density recording. In order to accurately reproduce data, it is necessary to accurately control the shape of the mark and the position of the edge. Further, in order to make uniform the shapes of the marks even if the lengths of marks are different, the multi-pulse recording method, which forms a recording mark with a pulse sequence including plural recording pulses, is widely used. That is, uniform mark shapes are formed by forming marks by repeating the cycle of heating and cooling and coupling the marks. This method is also used in recordable media of the dye system type.
Incidentally, with the recent demand for high-speed recording and large capacity storage, various recording methods have been proposed. One of the methods is making recording power to have multiple levels.
For example, in CDs, the pulse of an extra recording power Pwex is added to the front edge of a recording pulse as shown in FIG. 4(C), thereby correcting irregularity of mark shapes caused by insufficient thermal storage effect in a recording medium immediately after application of recording power (see FIG. 4(d)).
In addition, as shown in FIG. 8(c), an extra recording pulse of the extra recording power Pwex may be added to the rear edge as well as the front edge. Further, as shown in FIG. 8(d) and (e), the extra recording power Pwex may be added to the recording power of a specific pulse (e.g., the front pulse or the last pulse) of multiple pulses. These methods are also applied for recording mark edge position control or recording mark shape control.
Thus, in such multi-level recording methods, of course, accurate shapes and positions of marks cannot be formed if the extra recording power Pwex as well as recording power Pw are not appropriate values with respect to a recording medium.
Hence, in order to improve compatibility between a recording medium and a recording apparatus, it is preferable to perform the OPC as mentioned above. However, conventionally, an optimum recording power Pw is obtained by performing test writing while maintaining a predetermined proportional relationship between the extra recording power Pwex and the recording power Pw (Pwex/Pw=constant), or while varying the recording power Pw and maintaining the extra recording power Pwex to be a predetermined value (Pwex=constant).
With such OPC methods, however, in a case where there is variation in a recording medium or a recording apparatus (that is, variation in a recording pulse waveform due to variation in a LD driver), the relationship between the recording power Pw and the extra recording power Pwex is not maintained to be constant, and the extra recording power Pwex calculated in the aforementioned manner is not an appropriate value. Accordingly, the accuracies of the mark shape and the mark position are degraded, which causes a data error. In addition, even in the same recording medium, if the recording speed is different, then the relationship between the appropriate recording power Pw and the extra recording power Pwex is different.